Feynman diagrams: curved arrow to use into feyn package

Question

I wanted to draw the same figure of this question Hartree Fock Feynman diagrams using feyn package:

The curved arrow are specific of feynmp package for me complicated because I have not understood many commands and the style of this package.

I'm not able to draw the circle with curved arrow like the first picture.

Is there a possibility using feyn package?

Answer 1

This is a bit of a hacky attempt on my part so I am sure you can improve on it, but

\documentclass[12pt]{standalone}
\usepackage{feyn, graphicx}
\begin{document}
$\Diagram{& \ , {\rotatebox{80}{$\feyn{a}$}}!c!^{\rotatebox{-105}{$\feyn{a}$}} & \
  \mbox{$\Sigma_{HF}(\mathbf{p}, \omega) = $ } & fs gv fs \ + \ fglS a f }$
\end{document}

Also, as a side note: It seems like the \feyn package does some weird things with how you center rotations with \rotatebox. It generally ignores the [origin = ] command. If you want to rotate an arrow like \feyn{a} and keep it roughly on the same line you actually need to add a phantom object, so something like \rotatebox[origin=c]{180}{$\feyn{a}$\phantom{a}} gets the job done better than \rotatebox[origin=c]{180}{$\feyn{a}$}. (Kind of weird, but I am sure the answer is buried somewhere in the package itself.)

---

I moved the arrows a little bit vertically using the \raisebox command. (Turns out I was using it wrong or this would have been my original answer.)

\documentclass[12pt]{standalone}
\usepackage{feyn, graphicx}
\begin{document}
$\Diagram{& \ , \raisebox{.5mm}{\rotatebox{75}{$\feyn{a}$}}!c!\raisebox{1.5mm}{\rotatebox{-105}{$\feyn{a}$}} & \
  \mbox{$\Sigma_{HF}(\mathbf{p}, \omega) = $ } & fs gv fs \ + \ fglS a f }$
\end{document}